230v motor space heater element on 208v supply????

[emiller233]

working on a project where the mechanical guys ordered a motor with a space heater in it. The motor will be running on 480V, and the space heater on 208V. Apparently that combo was discontinued by the MFGR so they ordered it with a 230v heater in it and they didn't feel like telling anyone... so my question is, is it ok to use the 230v space heater on 208v?

the space heater is rated at 230v so +/-10% variance drops me to 207v. so I THINK im good on 208VAC :?

I haven't had any luck finding the heater info on their website yet, but this is the motor info
BALDOR VEM3615T + M21A
https://www.baldor.com/catalog/VEM3615T#tab="specs"

 

[infinity]

I don't see a problem but I guess someone could argue that it's only listed for use a 230 volts. You will get less heat if you run a 230 volt heater at 208 volts.

 

[Jraef]

I don't see a problem but I guess someone could argue that it's only listed for use a 230 volts. You will get less heat if you run a 230 volt heater at 208 volts.

To that point, if the heater is rated for 250W at 230V, it will drop to about 205W at 208V. But most of the time, motor space heater sizes are a S.W.A.G. anyway; all you need to do is keep the motor at or above the dew point without damaging the insulation. How much heat that takes depends a lot on the dew point, which changes with humidity anyway. So the trick is to over shoot what might be necessary by more than enough, while still avoiding damaging the insulation. +-20% probably will not make that much of a difference.

 

[Besoeker3]

I don't see a problem but I guess someone could argue that it's only listed for use a 230 volts. You will get less heat if you run a 230 volt heater at 208 volts.

Yes, true. I suppose the question is whether that matters. In many cases the space heater is thermostatically controlled which would mean it would be on for longer.
Probably not a problem..

 

[emiller233]

This will be going on to a hydraulic pump motor. There is also a heater for the hydraulic fluid in the reservoir.
The way the customer is controlling it now is when the heater is on for the tank fluid, then the space heater is on for the motor space heater as well. They have both heaters running off of a single contactor,. There is a temperature control on the tank for the fluid, but that is it.
This is replacing an existing system, so I guess they're fine with the control philosophy of the heaters

 

[LarryFine]

You will get less heat if you run a 230 volt heater at 208 volts.

Almost exactly 75% of rated wattage.

 

[Dennis Alwon]

Almost exactly 75% of rated wattage.

Isn't it 75% at 240 volts to 208--

 

[infinity]

Isn't it 75% at 240 volts to 208--

That was my recollection, the 230-208 reduction would be less loss in heat.

 

[LarryFine]

Isn't it 75% at 240 volts to 208--

A resistive load that is designed for 240v will run at approximately 75% of its rated power when supplied by 208v, because it is a constant-impedance type of load.

If you modify equipment that was designed for 240v to produce the same power when supplied by 208v, the resistance will be lower, which means more current.

A motor, on the other hand, will attempt to use more current when supplied by a lower voltage, because a motor is (or attempts to be) a constant-power load.

 

[infinity]

A resistive load that is designed for 240v will run at approximately 75% of its rated power when supplied by 208v, because it is a constant-impedance type of load.

If you modify equipment that was designed for 240v to produce the same power when supplied by 208v, the resistance will be lower, which means more current.

A motor, on the other hand, will attempt to use more current when supplied by a lower voltage, because a motor is (or attempts to be) a constant-power load.

I think that Dennis was asking about the heater in the OP which is 230 volts not 240 volts.

 

[LarryFine]

I think that Dennis was asking about the heater in the OP which is 230 volts not 240 volts.

My bad. That would result in around 81% of rated power.

 

[emiller233]

where does the 81% come from?

 

[kwired]

If want to be precise on 230 vs 240 one must also consider if the 208 source actually operates at 208. Around here 208 nominal service at no load will measure 213 to 216 most of the time.

 

[Jraef]

where does the 81% come from?

In a fixed resistance circuit (as a heater element is), power (kW) varies by the square of the voltage change. 208/230V = .904, then .904 squared is .817, so 82% (or 81% if you don't round up...)

Those that came up with 75% are using 240V instead of 230V. Same issue, but they are basing it on a 240V SUPPLY, I was basing it on the actual stated RATING of the motor heater element being 230V. You would not base the heating power change on a 240V supply, because that is not what you HAVE. You HAVE the heating element and if it says it was 230V, then that's what it is.

 

[kwired]

In a fixed resistance circuit (as a heater element is), power (kW) varies by the square of the voltage change. 208/230V = .904, then .904 squared is .817, so 82% (or 81% if you don't round up...)

Those that came up with 75% are using 240V instead of 230V. Same issue, but they are basing it on a 240V SUPPLY, I was basing it on the actual stated RATING of the motor heater element being 230V. You would not base the heating power change on a 240V supply, because that is not what you HAVE. You HAVE the heating element and if it says it was 230V, then that's what it is.

Those that came up with 75% also basing it on 240 rating and 208 actual input, if the "208 nominal" is actually running at 214, then that 75% will be a little lower than actual output.

Allowed tolerances in the equipment could vary things a little also.

 

[emiller233]

great info as always!!!
thanks everyone!